Linux Pocket Guide, 2nd Edition

Name

who — stdin  stdout  - file  -- opt  --help  --version

Synopsis

who [options] [filename]

The who command lists all logged-in users, one user shell per line:

$ who
smith    pts/0    Sep  6 17:09 (:0)
barrett  pts/1    Sep  6 17:10 (10.24.19.240)
jones    pts/2    Sep  8 20:58 (192.168.13.7)
jones    pts/4    Sep  3 05:11 (192.168.13.7)

Normally, who gets its data from the file /var/run/utmp. The filename argument can specify a different data file, such as /var/log/wtmp for past logins or /var/log/btmp for failed logins.^[17]

Useful options

-H	Print a row of headings as the first line.
--lookup	For remotely logged-in users, print the hostnames of origin.
-u	Also print each user’s idle time at his/her terminal.
-T	Also indicate whether each user’s terminal is writable (see mesg in Instant Messaging). A plus sign means yes, a minus sign means no, and a question mark means unknown.
-m	Display information only about yourself, i.e., the user associated with the current terminal.
-q	Quick display of usernames only, and a count of users. Much like the users command, but it adds a count.

^[17] If your system is configured to log this information.